TOKYO - Ministop Co, Japan's fifth-largest convenience store, plans to bid for South Korea's Buy The Way, which has been put up for sale by private equity firm Unitas Capital, three sources familiar with the matter said.

The sale of Buy The Way, South Korea's fourth-largest convenience store chain, is expected to fetch about $200 million-$300 million, two of the sources said, speaking on condition of anonymity as the negotiations are not public.

A unit of Seven & I Holdings, Japan's largest retailing group, may submit a separate bid together with South Korea's Lotte Group, one of the sources said.

Spokesmen for Ministop and Seven & I declined to comment while a spokesman for Lotte Group, whose unit operates Seven-Eleven outlets in South Korea under a license, said: We are not reviewing anything right now.

Unitas could not be immediately reached for comment.

Initial bids are due on Wednesday, according to two of the sources.

Japanese convenience stores have been keen to expand in fast-growing Asian countries with their domestic market saturated and unlikely to grow due to the country's dwindling birthrate and an ageing population.

FamilyMart, Japan's third-largest convenience store, now has more stores overseas than in Japan.

South Korea's convenience store market grew 17 percent to 6.5 trillion won last year and there are nearly 14,000 stores.

FamilyMart has about 4,400 outlets and controls about a third of the market. Seven-Eleven has 16 percent of the market while the market share of Ministop is about 9 percent, according to media estimates.

The winner of the bid would gain Buy The Way's 1,400 stores. (Reporting by Ritsuko Shimizu and Taro Fuse; Writing by Nathan Layne; Editing by Hugh Lawson)